These regimens can reduce verapamil absorption. Closely monitor the clinical response of the patient and adjust the verapamil dose as needed.

Aspirin

Risk of bleeding may be increased compared with aspirin alone. Monitor bleeding times.

Barbiturates (eg, phenobarbital)

Verapamil Cl may be increased, reducing plasma concentrations and the pharmacologic effect. Monitor the clinical response of the patient and adjust the verapamil dose as needed.

Beta-blockers (eg, metoprolol)

May result in increased hypotension and adverse reactions because of additive depressant effects on myocardial contractility or AV conduction. Avoid verapamil in patients with any degree of ventricular dysfunction if they are receiving beta-blockers.

Buspirone

Pharmacologic and adverse reactions may be increased by verapamil. Closely monitor the clinical response of the patient and adjust buspirone dose as needed.

Calcium salts

Clinical effects and toxicities of verapamil may be reversed. Unless calcium salts are being used as an antagonist in treating verapamil overdose, use calcium salts with caution in patients taking verapamil.

The interaction between cimetidine and chronically administered verapamil has not been studied. Variable results on Cl have been obtained in acute studies of healthy volunteers; Cl of verapamil was either reduced or unchanged. If an interaction is suspected, adjust the verapamil dose as needed.

Clonidine

Synergistic effects resulting in sinus bradycardia have been reported in association with coadministration of clonidine and verapamil. Monitor heart rate during concurrent use of verapamil and clonidine.

Colchicine

Colchicine plasma concentrations may be elevated by verapamil, increasing the risk of toxicity. Colchicine dosing adjustment may be needed for patients also receiving verapamil. Use with caution and closely monitor for colchicine toxicity. The recommended colchicine dose for the treatment of a gout flare in patients receiving verapamil is 1.2 mg for one dose. A 3-day lapse should occur before subsequent colchicine administration. The recommended max colchicine dose for treatment of familial Mediterranean fever in patients receiving verapamil is 1.2 mg daily.

Cyclosporine

Increased cyclosporine levels may result, increasing the pharmacologic effect and risk of toxicity. However, verapamil may be nephroprotective when given before cyclosporine. Monitor cyclosporine levels and adjust dose as needed.

Verapamil plasma levels may be elevated, increasing the pharmacologic effects and adverse reactions. Closely monitor cardiac function and adjust the dose as needed.

Dantrolene

Hyperkalemia and myocardial depression has been reported in a patient following coadministration of oral verapamil and IV dantrolene. Monitor serum potassium and cardiac function.

Digitalis glycosides

Increased serum digoxin or digitoxin levels may occur. Monitor digoxin levels and adjust dose as needed. Because both drugs slow AV conduction, also monitor for AV block or excessive bradycardia. If possible, control patients with mild ventricular dysfunction with optimum doses of digitalis and/or diuretics before starting verapamil treatment.

Disopyramide

Do not use 48 h before or 24 h after verapamil.

Dofetilide

Risk of life-threatening ventricular arrhythmias, including torsades de pointes, may be increased. Coadministration with verapamil is contraindicated.

Doxorubicin

Doxorubicin serum concentrations may be elevated. Monitor the clinical response of the patient and adjust treatment as needed.

Dronedarone

Dronedarone plasma concentrations and pharmacologic effects may be increased. Verapamil may enhance the electrophysiologic effects of dronedarone. Also, verapamil plasma concentrations and pharmacologic effects may be increased. Initiate verapamil at low doses in patients receiving dronedarone. Monitor the ECG. Increase the verapamil dosage if the ECG demonstrates tolerability.

Eletriptan

Eletriptan plasma concentrations may be elevated, increasing the pharmacologic effects and risk of adverse reactions. Closely monitor for signs of eletriptan adverse reactions.

Eplerenone

Verapamil may elevate eplerenone plasma concentrations, increasing the pharmacologic effects and risk of toxicity. Closely monitor the clinical response of the patient and adjust the eplerenone dose as needed.

Everolimus

Verapamil may elevate everolimus plasma concentrations, increasing the pharmacologic effects and risk of adverse reactions. If coadministration cannot be avoided, closely monitor everolimus blood concentrations when verapamil is started or stopped. Adjust the everolimus dose as needed.

Fentanyl

Verapamil may elevate fentanyl plasma concentrations, increasing the pharmacologic effects and risk of toxicity. When fentanyl and verapamil are coadministered, the manufacturer recommends closely monitoring patients for an extended period of time. Dosage increases should be done conservatively.

Flecainide

May prolong AV conduction. Concurrent therapy with flecainide and verapamil may result in additive negative inotropic effect and prolongation of atrioventricular conduction. Carefully monitor cardiac function and adjust treatment as needed.

Grapefruit juice

Verapamil plasma concentrations may be elevated. This increase is not expected to have any clinical consequences.

Plasma concentrations of certain HMG-CoA reductase inhibitors may be elevated. In addition, verapamil concentrations may be elevated, increasing the pharmacologic effects and risk of toxicity. If coadministration cannot be avoided, administer a conservative dose of the HMG-CoA reductase inhibitor. Advise patients to report any unexplained muscle pain, tenderness, or weakness. Monitor the clinical response and for adverse reactions to verapamil. Adjust the dose as needed.

Hydantoins (eg, phenytoin)

The pharmacologic effects of verapamil may be decreased. Monitor CV status closely. Adjust dose as needed.

Midazolam plasma concentrations may be elevated, increasing and prolonging CNS depression. The dosage of midazolam may need to be decreased when given with verapamil. Monitor the patient for possible prolonged sedation.

Coadministration may increase the therapeutic and adverse reactions of quinidine. Use quinidine with verapamil only when no alternatives exist. Closely monitor quinidine serum levels and cardiac effects. Verapamil may counteract the effects of quinidine on AV conductions. In patients with hypertrophic cardiomyopathy, coadministration of verapamil and quinidine may cause clinically important hypotension. Avoid concurrent use of verapamil and quinidine in patients with hypertrophic cardiomyopathy.

Ranolazine

Ranolazine plasma concentrations may be elevated, increasing the pharmacologic effects and risk of toxicity. Limit the dosage of ranolazine to 500 mg twice daily. During verapamil coadministration, closely monitor for signs of ranolazine toxicity, including QT interval prolongation.

Rifampin

Loss of effectiveness of oral verapamil may occur. Closely monitor CV status and adjust the verapamil dose as needed.

Risperidone

Risperidone plasma concentrations may be elevated, increasing the pharmacologic effects and risk of adverse reactions. In patients receiving risperidone, closely monitor the clinical response of the patient after starting, stopping, or changing the verapamil dose. Adjust the risperidone dose as needed.

St. John’s wort

Verapamil plasma concentrations may be reduced, decreasing the efficacy. If St. John’s wort cannot be avoided, assess the clinical response of the patient to verapamil when St. John’s wort is started or stopped. Adjust the verapamil dose as needed.